In a wireless cellular network system, there is typically a base station in communication with a User Equipment (UE) in each cell. Various user equipments include a mobile phone, a notebook, a Personal Digital Assistant (PDA), etc. Prior to commence of a data transmission process, the base station may transmit a reference signal (e.g., a pilot signal) to the user equipment, and the user equipment may derive a channel estimation value from the reference signal. The reference signal is a known signal sequence transmitted at a specific time and a specific frequency as prescribed, and the quality of channel estimation may be influenced by interference, noise and other factors.
Typically user equipments are located at different geographic positions and are subjected to different received signal strength and different noise and interference strength. Thus some user equipments may communicate at a higher rate, for example, a user equipment located at the center of the cell, and some other user equipments can only communicate at a lower rate, for example, a user equipment located at the edge of the cell. In order to make full use of a transmission bandwidth of a user equipment, data is transmitted to the user equipment preferably in a format matching a channel condition of the user equipment, and a technology to match the format, in which data is transmitted to the user equipment, with a channel condition of the user equipment is referred to link adaptation.
In order to assist the base station in link adaptation, the user equipment needs to report a Channel Quality Indicator (CQI) according to a channel condition of the user equipment. The CQI reported by the user equipment corresponds to a specific time-frequency resource, that is, the CQI reported by the user equipment represents a transmission capacity on the time-frequency resource. In order to calculate the CQI, the user equipment needs to measure interference I and noise power N0 to which it is subjected. For example, a straightforward CQI calculation formula is:
      CQI    =          Q      ⁡              (                  P                      I            +                          N              0                                      )              ,
Where P is received signal power of the user equipment, and Q(•) is a quantization function; and in practice, the user equipment may measure the sum of I and N0, i.e., I+N0.
In the prior art, the technology of Coordinated Multipoint Transmission/Reception (CoMP) refers to coordinated scheduling or joint transmission of multiple geographically separated transmission points for the purpose of lowering mutual interference and improving the quality of a signal received by a user to thereby effectively improve the capacity of a system and the spectral efficiency of an edge user. The multiple separated transmission points typically refer to base station devices of multiple cells or possibly different base station devices in the same cell.
Coordinated scheduling refers to that the respective base stations coordinate time, frequency and space resources between the cells to allocate mutually orthogonal resources for different UEs to thereby avoid mutual interference. Inter-cell interference is a predominant factor restricting the performance of a cell edge UE, and inter-cell interference can be lowered through coordinated scheduling to thereby improve the performance of the cell edge UE. Referring to FIG. 1, for example, coordinated scheduling of three cells can schedule three UEs possibly interfering with each other onto mutually orthogonal resources to thereby effectively avoid interference between the cells.
Joint transmission refers to concurrent transmission of data from multiple cells to a UE to thereby enhance a received signal of the UE. Referring to FIG. 2, for example, data is transmitted from three cells to the same UE on the same resource, and the UE receives signals from the multiple cells concurrently. On one hand, superposition of the useful signals from the multiple cells can improve the quality of the signals received by the UE. On the other hand, interference to which the UE is subjected can be lowered to thereby improve the performance of a system.
In Long Term Evolution (LTE) and LTE-Advanced (LTE-A) systems, a UE estimates channel information of a base station to the UE (e.g., a signal matrix, interference, noise, etc.) according to a Cell-specific Reference Signal (CRS) or a Channel State Information-Reference Signal (CSI-RS) of a serving cell, calculates a CQI, and feeds the CQI back to the base station, possibly together with a Pre-coding Matrix Index (PMI) and an Rank Indicator (RI). The base station can perform scheduling, resource allocation, Modulation and Coding Scheme (MCS) selection and other operations using the feedback of the CQI to thereby improve the spectral efficiency. In order to support multipoint coordinated transmission, a report of channel information needs to be further enhanced. The UE estimates channel information of cells included in a preconfigured measurement set to the UE according to CRSs or CSI-RSs transmitted from the respective cells, and next the UE directly scalar-quantizes or vector-quantizes the channel information and then feeds it back to the base stations, and the base stations perform pre-coding matrix calculation, multi-user pairing, MCS selection and other operations according to the channel information fed back from the UE.
In the CoMP technology of a Time Division Duplex (TDD) system, a base station can derive uplink channel information from a Sounding Reference Signal (SRS) transmitted from a UE and derive downlink channel information by the reciprocity of uplink and downlink channels. In the existing TDD system, the base station can not accurately select an MCS and perform frequency-domain scheduling for the UE simply according to the channel information derived from the SRS because the uplink and the downlink are subjected to typically different interference and the base station can not accurately predicate interference to which the UE is subjected; and on the other hand, in the existing TDD system, the base station can not accurately select an MCS and perform frequency-domain scheduling for the UE even according to the channel information fed back from the UE because an interference level of an adjacent cell before scheduling is different from that after scheduling due to the use of the CoMP technology as well as beam shaping and other schemes so that the UE can not predicate a changed interference level after scheduling upon feeding back the channel information.
In view of this, it is desirable to redesign a corresponding CoMP-based channel information calculation and report solution.